Antidepressants and Small Animals: What Should You Know?
WSAVA/FECAVA/BSAVA World Congress 2012
Kersti Seksel, BVSc(Hons), MA(Hons), FACVSc, DACVB, CMAVA, DECVBM-CA, MRCVS
Sydney Animal Behaviour Service, Seaforth, Australia


Medication for behavioural problems should not be viewed as a quick fix or a silver bullet. The decision to use medication (or not) depends on the diagnosis and this should include a thorough physical work-up, blood work and a behavioural assessment. Medications are not generally indicated for problem behaviours, only for behaviour problems so it is important that veterinarians understand the rationale for prescribing psychotropic medication.

Many of the medications commonly used are not registered for this purpose in companion animals. As more and more medications are registered for use in animals it is important that veterinarians are familiar with these medications and the research that supports their use. This allows veterinarians to make an informed decision about which medication to use, why and when.

Much information regarding psychotropic medication is derived from human literature. However, drug metabolism and receptor effects vary between species. This can lead to inaccurate assumptions with respect to dose, duration of effect, contraindications and side effects. It is the veterinarian's responsibility to be familiar with these factors before prescribing medication. Therefore, medications that are licensed for use in pets (e.g., clomipramine, fluoxetine) should be considered first as there are data with respect to safety, efficacy, side effects, contraindications, toxicity and pharmacokinetics. In addition, the technical support available from the manufacturer provides additional expertise, especially in the event of adverse reactions.

The final choice of medication is up to the veterinarian and medication should be selected using the evidence available combined with the veterinarian's expertise as well as information about the patient, client and the problem.

Clients need to understand that behaviour modification as well as environmental management are both necessary. Behaviour problems take considerable time to manage. Medication may be needed for the life of the patient just as in cases involving metabolic diseases for example, diabetes.

Once the behaviour is managed to the owner's satisfaction, the lifelong commitment from the owner and continued support from the veterinarian are still required.

Why Use Medication?

The rationale for using psychotropic medication is based on their purported neurochemical actions in the brain. Many medications are now used to modify behaviour in companion animals.

Medications may influence neurotransmitters in three main ways. They may act:

 Presynaptically and affect the presynaptic action potential, synthesis, storage, metabolism, release or re-uptake.

 On the enzymes that deactivate the neurotransmitter.

 Post-synaptically and affect binding to receptors by acting as agonists or antagonists or actually modify receptors.

Why is a Diagnosis Important?

Before prescribing medication for any condition it is important to have a diagnosis to support the decision to medicate. Behavioural medicine issues should not be approached any differently from the way that veterinarians approach internal medicine or dermatological problems.

A behavioural diagnosis should be based on a thorough physical examination and behavioural history. This should always include diagnosis and treatment of any concurrent physiological problems.

Pretreatment Screening: Blood Tests, Urine Tests, Other Medications Etc.

Blood tests prior to prescribing medication are always recommended, especially in very old or young animals or those with a previous history of medical problems. A minimum database should include complete blood count (CBC), biochemistry panel and urine test. As most of the medications are metabolised through the liver and then excreted via the renal system, liver and kidney enzyme level monitoring is important prior to and during medication.

These tests may need to be repeated, after starting medication, depending on the animal, the medication and effects seen. All animals on long-term medication should be reassessed and blood work re-evaluated every 6–12 months depending on age and medical history.

It is also important to question owners about what other medications they may be administering to their pet. This includes the use of natural remedies or homeopathic medications as many owners do not appreciate that these may also have significant effects on their pet as well as interact with the medications prescribed by the veterinarian.

When to Use Psychotropic Medication

There are several categories of behavioural problems where psychotropic medications have proven to be useful. These include anxiety-related problems (including fears and phobias), obsessive compulsive behaviours, some types of aggression and geriatric behaviour problems.

The treatment of non-specific signs (such as excessive vocalisation, aggression or inappropriate elimination) by using medication is not acceptable and this approach will ultimately lead to treatment failures.

What if the Medication Does Not Work?

Owners often feel that the medication has been ineffective. This may happen for many reasons including:

 No diagnosis was made.

 Incorrect diagnosis was made.

 Incorrect medication was selected.

 An inadequate length of time was allowed for the treatment programme to take effect.

 Medication has been used as 'stand alone' therapy when it should have been combined with a behaviour-modification programme and environmental management.

 The owner was unable to medicate the pet.

In some cases the effects of medication can only be seen when the medication has been stopped.

What Do Owners Need To Know About Medication?

 Medication may take 6–8 weeks to reach therapeutic blood levels. Owners need to appreciate that the effects will not be immediate.

 The medication or the dose may need to be changed as the management/treatment progresses.

 The minimum time required for an animal to receive medication is usually 6 months.

 Medication may be needed lifelong. This needs to be discussed with owners in advance.

 Medication should never be suddenly stopped. It should always be reduced gradually to avoid a rebound affect. Owners should be warned of this whenever prescribing medication.

 Medication should only be stopped, have a change in dose or medication changed on veterinary advice and under veterinary supervision.

Common Psychotropic Medications

Medications that have been used to treat behavioural problems include the benzodiazepines, tricyclic antidepressants (TCAs), antihistamines, azaparones, selective serotonin re-uptake inhibitors (SSRIs), serotonin antagonist reuptake inhibitors (SARIs) and beta-blockers. Only antidepressants will be considered in this paper.

Tricyclic Antidepressants

Clinical Uses

 Cats: Spraying, feline lower urinary tract disease (FLUTD), overgrooming, anxiety, intercat aggression, obsessive compulsive disorders.

 Dogs: Impulse control aggression, fear aggression, separation anxiety, obsessive compulsive disorders, acral lick granulomas, fears and phobias such as thunderstorm phobia.

Side Effects

Short-term lethargy or sedation, mild and intermittent vomiting (usually transient) and increases or decreases in appetite, dry mouth, constipation, urinary retention, tachycardia, cardiac arrhythmia and decreased tear production.


High doses have been associated with increased liver enzymes, hepatotoxicity and convulsions. They should not be used in animals with cardiac dysrhythmia, urinary retention, narrow angle glaucoma, seizures or within 2 weeks of mono-amine oxidase inhibitor (MAOI) administration. These medications may also interfere with thyroid medications and should be used with caution in these patients.



 Cats: 0.5–1.0 mg/kg orally q24h

 Dogs: 1–3 mg/kg orally q12–24h


 Cats: 0.25–0.5 mg/kg orally q24h

 Dogs: 1–2 mg/kg orally q12h 2 weeks, then 3 mg/kg orally q24h if needed


 Cats: 0.5–1.0 mg/kg orally q12–24h

 Dogs: 3–5 mg/kg orally q12h (for acral lick dermatitis)

Selective Serotonin Re-Uptake Inhibitors

As the name implies they are selective for serotonin and lack the anticholinergic and cardiovascular side effects of the TCAs.

Clinical Uses

 Cats: Spraying, some types of aggression, obsessive compulsive disorders.

 Dogs: Obsessive compulsive disorders, separation anxiety, generalised anxiety or global fear, some types of aggression.

Side Effects

Reported side effects include liver changes, gastrointestinal disturbances and rashes, while nausea, lethargy, weight loss, tremors and agitation have been reported in people.


They should not be used concomitantly with MAOIs (serotonin syndrome) and at least 2 weeks should be allowed as a washout period between SSRI and MAOI therapy, and 5 weeks for fluoxetine.



 Cats: 0.5 mg/kg orally q12–24h

 Dogs: 1mg/kg orally q12h (maximum 4 mg/kg every 24 hours)


 Cats: 1 mg/kg orally q12h

Serotonin Antagonist Reuptake Inhibitor

Trazodone is a serotonin 2A antagonist reuptake inhibitor (SARI) that blocks post-synaptic serotonin-5HT and alpha-adrenergic receptors. Trazodone hydrochloride is an antidepressant chemically unrelated to tricyclic, tetracyclic or other known antidepressant agents. It is used in human medicine as an antidepressant, anti-obsessional and anti-anxiety agent.

Clinical Uses

 Dogs only, not cats: As an adjunctive agent in combination with selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) for anxiety, obsessive compulsive disorders, separation anxiety, generalised anxiety or global fear, some types of aggression.

Side Effects

Reported side effects in dogs include vomiting, gagging, colitis, increased excitement, sedation, increased appetite and perceived behavioural disinhibition.


Trazodone is contraindicated in patients with known hypersensitivity to trazodone.



 Dogs: Ranges from 1.7–13.4 mg/kg with an average of 6.6 mg/kg


1.  Gruen ME, Sherman B. Use of trazodone as an adjunctive agent in the treatment of canine anxiety disorders: 56 cases (1995–2007). Journal of the American Veterinary Medical Association 2008;233(12):1–6.

2.  Landsberg G, Hunthausen W, et al. Handbook of Behaviour Problems of the Dog and Cat. Oxford: Butterworth Heinemann. 2003.

3.  Overal KL. Clinical Behavioral Medicine for Small Animals. St Louis: Mosby, 1997.

4.  Rang HP, Dale MM, et al. Pharmacology. New York: Churchill Livingstone, 1995.

5.  Seksel K. Behavior-modifying drugs. In: Maddison JE, Page SW, Church DB, eds. Small Animal Clinical Pharmacology. 2nd ed. London: WB Saunders. 2008:126–147.


Speaker Information
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Kersti Seksel, BVSc(Hons), MA(Hons), FACVSc, DACVB, CMAVA, DECVBM-CA, MRCVS, Registered Veterinary Specialist, Beha
Sydney Animal Behaviour Service
Seaforth, Australia